The pursuit of low-carbon binders as alternatives to Portland cement has sparked interest in developing alkali-activated materials (AAM).¹ Using municipal solid waste incineration (MSWI) bottom ash as precursor for AAM has attracted increasing attention as it offers a sustainable, resource-efficient solution to mitigate the environmental impacts associated with the landfill of MSWI bottom ash. However, the varying properties of MSWI bottom ash present challenges in its wide application as AAM precursor. This review provides a comprehensive overview of advances in MSWI bottom ash-based AAM,² with a particular focus on the relationship between the physicochemical properties of MSWI bottom ash and the engineering properties of MSWI bottom ash-based AAM. This work consolidates the most up-to-date understanding of the reaction mechanism and reaction products of MSWI bottom ash, along with the existing knowledge about mix design and microstructure formation of MSWI bottom ash-based AAM. The factors influencing the engineering properties of MSWI bottom ash-based AAM are detailed, and the environmental impacts of MSWI bottom ash-based AAM are reviewed. Ultimately, this review provides recommendations for the standardized and effective use of MSWI bottom ash as AAM precursor.@en

Alkali-activated foams are ceramic-like materials prepared at near-ambient temperature. This study investigates them for point-of-use water disinfection, thus providing an alternative to ceramic filters fired at a high temperature. Alkali-activated foams with different compositions were characterized for the porosity, mechanical strength, shrinkage, and microstructure. The optimized foam, employing metakaolin as the raw material, was coated with a colloidal Ag solution. The disinfection performance and leaching behavior of the foams was followed in a continuous 10 week experiment, where clean water with a weekly pulse of contaminated water was distributed through the foam. The average inactivation of Escherichia coli with the Ag-coated foam was 2.84 log₁₀, which was 1.27 units higher compared to foam without Ag. A quantitative polymerase chain reaction analysis and metagenomic sequencing verified that foams with and without Ag were both capable of reducing the microbial load. Furthermore, the changes induced by the foam with Ag on the microbial community composition, antibiotic resistome, and metal and biocide resistomes were significant. The leached concentrations of Ag, Na, Si, and Al were in accordance with the drinking water guidelines. Finally, a life cycle assessment indicated the possibility of reducing the global warming potential and the total embodied energy in comparison with a conventional ceramic filter.

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Municipal solid waste incineration (MSWI) bottom ash, due to its high mineral content, presents great potential as supplementary cementitious material (SCM). Weathering, also known as aging, is a treatment process commonly employed in waste management to minimize the risk of heavy metal leaching from MSWI bottom ash. Using weathered MSWI bottom ash to produce blended cement pastes is considered as a high-value-added and sustainable waste disposal solution. However, a critical challenge arises from the metallic aluminum (Al) in weathered MSWI bottom ash, which is known to induce detrimental effects such as volume expansion and strength loss of blended cement pastes. While most metallic Al in weathered MSWI bottom ash can be removed with eddy current separators in metal recovery plants, the residual metallic Al, owing to its small particle size, cannot be removed with the same technique. This study is dedicated to addressing this issue. An in-depth analysis was conducted on residual metallic Al embedded in weathered MSWI bottom ash particles, aiming to guide the removal of this metal. This analysis revealed that mechanical removal was the most suitable method for extracting metallic Al. The specific processes and mechanisms underlying this method were elucidated. After reducing metallic Al content in weathered MSWI bottom ash by 77 %, a significant improvement in the quality of blended cement pastes was observed. This work contributes to the broader adoption of mechanical treatments for removing residual metallic Al from weathered MSWI bottom ash and facilitates the application of treated ash as SCM.

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This research explored the microstructure formation and strength development of blended cement pastes prepared with municipal solid waste incineration (MSWI) bottom ash. A new sample preparation approach involving water treatment of MSWI bottom ash was developed to prevent sample cracking caused by the presence of metallic aluminum (Al) in bottom ash. The result showed that ions released during water treatment of MSWI bottom ash delayed cement hydration but promoted ettringite formation in blended cement pastes during the first day. Due to water treatment, the compressive strength of MSWI bottom ash blended cement paste increased to a level similar to that of Class F coal fly blended cement paste after 28 days. Blending water-treated MSWI bottom ash (WMBA) with cement promoted clinker hydration at later stages. The reaction products of WMBA in blended cement system were C-S-H gel and sodicgedrite, which contributed to strength development by filling the capillary pores.

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With the development of waste recovery techniques, previous research has revealed that coarse fractions of municipal solid waste incineration (MSWI) bottom ash (BA) after proper treatment could be applied in the construction sector, while the fines are seldom recovered in practice and normally landfilled. This study explores the potential application of fine MSWI BA (0–2 mm) as a supplementary cementitious material (SCM) in Portland cement (PC) mixtures. Mechanical and chemical pre-treatment approaches have been designed with various conditions to optimize the treating process. The chemical and mineralogical compositions, as well as the metallic Al content in BA were characterized before and after the pre-treatment. It was found that both methods are effective in removing the metallic Al content in BA, Moreover, BA derived from mechanical treatment exhibited more contribution to the hydration reaction in PC mixtures, as revealed by the amount of reaction products and mineral phases formed in hardened trial mixtures. BA obtained was further partially blended in PC mortars to evaluate the performance as compared to SCMs and inert fillers. It was found that treated BA resulted in a slight retarding effect on the reaction kinetics. Treated BA behaved better than the coal fly ash to contribute to the strength development, while the inclusion of BA did not lead to significant influences on the workability.

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In recent years, considerable attention has been given to the utilization of municipal solid waste incineration (MSWI) bottom ash as a mineral resource for construction materials. MSWI bottom ash is the primary residue discharged after incinerating municipal solid waste. The generation of MSWI bottom ash is increasing dramatically with the wide application of waste incineration techniques. Different methods have been proposed to improve the quality of MSWI bottom ash and make it suitable as supplementary cementitious material (SCM) or precursor for alkali-activated materials (AAM). However, there is no systemic guidance on how to select quality-upgrade treatments for MSWI bottom ash. When using MSWI bottom ash to prepare blended cement pastes and alkali-activated pastes, the optimal mix design is usually found by trial and error. Very little information is available in the literature regarding the reaction of MSWI bottom ash as SCM and AAM precursor. The contribution of MSWI bottom ash to the microstructure formation and strength development of blended cement pastes and alkali-activated pastes is not very well understood. The goal of this research is to develop knowledge that can be used to support the application of MSWI bottom ash as a mineral resource for construction materials. Based on this knowledge, a strategy for using MSWI bottom ash produced in the Netherlands (4-11 mm) as raw material to produce blended cement pastes and alkali-activated pastes is proposed. This research consists of the following parts: 1. Quality-upgrade treatments of as-received MSWI bottom ash As-received MSWI bottom ash cannot be used directly as SCM and AAM precursor due to its large particle size and presence of metallic aluminum (Al). Mechanical treatments consisting of grinding and sieving were studied and selected to reduce the particle size and the metallic Al content of as-received MSWI bottom ash. The effectiveness of the mechanical treatments used to reduce the metallic Al content of MSWI bottom ash is strongly influenced by the distribution of metallic Al in bottom ash particles. Most metallic Al separated during mechanical treatment comes from the coarse particles. The metallic Al embedded in the particles smaller than 0.5 mm is difficult to be removed via mechanical treatments (see Chapter 3). 2. Development and microstructure analysis of blended cement pastes and alkali-activated pastes The reactivity and leaching potential of mechanically treated MSWI bottom ash (MBA) are studied. This information is used in the development of blended cement pastes and alkali-activated pastes. A dissolution test is proposed to assess the reactivity of MBA as AAM precursor. The reactivity of MBA as SCM and AAM precursor is similar to that of Class F coal fly ash (FA), but much lower than that of blast furnace slag (BFS). The leaching of antimony (Sb) and sulfate from MBA is above the threshold value prescribed in Dutch Soil Quality Decree. The dosage of MBA in blended cement pasts and alkali-activated pastes should be controlled to prevent excessive leaching of contaminants into the environment (see Chapter 4). The reactivity of MBA is determined by the content and the chemical composition of its amorphous phase. The amorphous phase of MBA has a chemical composition within the same range as that of the amorphous phase of FA. Given that the reactivity of MBA is close to that of FA, previous experience with the mix design of Class F coal fly ash-based pastes is used as a reference for the mix design of MBA-based AAM. Additionally, thermodynamic modeling is used to predict the assemblage of reaction products and the composition of pore solution in alkali-activated MBA paste when changing the Na2O content in the activator. The modeling results are also used to guide the mix design of MBA-based AAM (see Chapter 4). When water treatment and NaOH solution treatment are part of the mixture preparation procedure, the compressive strength of the blended cement pastes and alkali-activated pastes made from MBA is close to that of the pastes prepared with the same amount of FA (Chapters 5 and 6). The metallic Al that cannot be removed during mechanical treatments can be oxidized by treating MBA in water or NaOH solution at room temperature. Apart from reducing metallic Al content, water treatment and NaOH solution treatment also slightly change the mineralogical composition of MBA. Blending water-treated MBA (WMBA) with Portland cement paste leads to changes in the reaction products and microstructure. WMBA delays clinker hydration on the first day but enhances clinker hydration at later ages. The reaction products of WMBA contribute to the strength development of blended cement pastes (see Chapter 5). NaOH solution-treated MBA (CMBA) is used together with BFS to prepare alkali-activated pastes. CMBA retards the reaction of BFS during the first seven days but promotes the reaction of BFS at later ages. Adding CMBA into alkali-activated pastes changes the reaction products and microstructure. The reaction products of CMBA contributes to the strength development of alkali-activated pastes (see Chapter 6). 3. Environmental impact assessment of blended cement pastes and alkali-activated pastes Compared with Portland cement paste, blended cement pastes and alkali-activated pastes prepared using MSWI bottom ash SCM and AAM precursor have lower environmental impacts, especially in the impact category of global warming (see Chapter 7). This research deepens the understanding of the reaction of MSWI bottom ash as SCM and AAM precursor. This study also demonstrates how to use MSWI bottom ash to prepare blended cement pastes and alkali-activated pastes by considering the chemical and physical properties of MSWI bottom ash. Since the MSWI bottom ash used in this research has chemical and mineralogical compositions within the same range as the MSWI bottom ash reported in the literature, the knowledge developed in this work stimulates the utilization of MSWI bottom ash produced in other regions as SCM and AAM precursor for construction materials. @en

Aimed to address the low utilization rate of steel slag (SS) and its challenge in resource utilization in China, this study developed ternary geopolymers made by high-content (50%) SS together with fly ash (FA) and granulated blast furnace slag (GBFS). The effects of GBFS content (0–40%) and curing methods (water curing, standard curing, sealed curing, and heat curing) on the working performance and microstructure of geopolymers were investigated. Microscopic analysis such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG-DTG), and scanning electron microscopy (SEM) were utilized to investigate the hydration process and products of geopolymers under different curing conditions and GBFS content. The results indicated that when the GBFS content increased from 0% to 40%, the fluidity of the mixture decreased by 11.7%, the initial setting time of the geopolymer slurry decreased by 76%, and the geopolymer mortar's 28d compressive strength increased from 31.9 MPa to 60.6 MPa. At room temperature, the geopolymer mortar's 28d compressive strength was higher under standard curing (70.8 MPa) compared to water curing (57.5 MPa) and sealed curing (68 MPa). The geopolymer mortar cured at 60 °C for 24 h exhibited the highest 28d compressive strength (76.3 MPa). However, excessively high curing temperatures or prolonged durations led to more shrinkage cracks and reduced the compressive strength. The microscopic analysis revealed that the main gel products of ternary geopolymer were C-(A)-S-H gel. The amount of gel products is directly related to the strength of geopolymers. The developed ternary geopolymer has the potential to promote the large-scale utilization of SS in the concrete industry, making a significant contribution to sustainable development.

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In recent years, the widespread application of waste incineration technology has led to an increased generation of municipal solid waste incineration (MSWI) bottom ash. There is growing interest in the use of MSWI bottom ash as a mineral resource to produce construction materials. The utilization potential of MSWI bottom ash is determined by its chemical and mineralogical compositions, which can vary from incineration plant to incineration plant, and even from batch to batch within a single incineration plant. The quality of MSWI bottom ash often needs to be improved before it can be used as supplementary cementitious material (SCM) and precursor for alkali-activated materials (AAM). This review summarizes the composition of MSWI bottom ash sourced from different regions and the proposed treatments for quality upgrades of MSWI bottom ash. The reactivity of MSWI bottom ash as SCM and AAM precursor is discussed. Finally, the challenges regarding the use of MSWI bottom ash as a mineral resource for the production of construction materials are examined and possible solutions are provided.

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This work evaluated the reactivity and leaching potential of municipal solid waste incineration (MSWI) bottom ash as supplementary cementitious material (SCM) and precursor for alkali-activated materials (AAM). The chemical composition of the amorphous phase in MSWI bottom ash was found to be in the same range as that of Class F coal fly ash. The reactivity of MSWI bottom ash as SCM and AAM precursor was tested to be much lower than that of blast furnace slag, but similar to that of Class F coal fly ash. The method of thermodynamic modeling was found useful in providing references for the mix design of MSWI bottom ash-based AAM. Grinding MSWI bottom ash into powder for the application of SCM and AAM precursor increased its leaching potential. Based on the findings of this study, recommendations were provided on how to use MSWI bottom ash to prepare blended cement pastes and AAM.

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In recent years, the rapid industrialization and urbanization led to the explosive growth of municipal solid waste incineration (MSWI) bottom ashes (BA) production. However, most of them are directly landfilled, which not only brings environmental burden but also results in loss of potential resources. Present researches have proved that MSWI BA could be utilized as a replacement in Portland cement concrete. However, several drawbacks such as volume expansion, leaching behaviour, and relatively lower strength have been reported. In this study, as-received BA was pretreated to remove the metallic aluminium which is responsible for the hydrogen-induced expansion when blended in OPC concretes. Subsequently, the treated BA samples were used as a substitution for cement at the replacement level of 10%. Micronized sand (M300) was selected as reference materials to investigate the role of treated BA in blended cement system, either as filler or binder material. In the experimental program, the hydration process of different mixtures was monitored by isothermal calorimeter and hydration products were determined by X-ray diffraction (XRD) and Thermalgravimetric analysis (TGA). Results showed that the pretreatment effectively removed the metallic aluminum in BA and no severe expansion or strength decrement were detected. The treated BA showed limited reactivity comparing with Portland cement, however, it still worked better than micronized sand as a filler substitution.@en

This study aims to investigate the influences of different grades of calcined clay on 3D printability, compressive strength (7 days), and hydration of limestone and calcined clay-based cementitious materials. Calcined clays that contained various amounts of metakaolin were achieved by blending low-grade calcined clay (LGCC) and high-grade calcined clay (HGCC) in three different proportions. The results revealed that increasing the HGCC% ranging from 0 wt% to 50 wt% in calcined clay could: (1) increase the flow consistency; (2) impressively improve the buildability, and reduce the printability window of the fresh mixtures; (3) enhance and accelerate the cement hydration. The reduction of mean interparticle distance induced by increasing HGCC% may be the primary reason for the enhancement of buildability and very early-age hydration. However, increasing HGCC% led to an increase of air void content in the interface region of the printed sample, which weakened the compressive strength of the printed sample at 7 days. Besides, it confirmed that the cold-joint/weak interface was easily formed by using the fresh mixture with a high structuration rate.@en

At present, most municipal solid waste incineration (MSWI) bottom ash, as being disposed of as waste, is directly landfilled, raising concern about the environmental issue and potential loss of resources. Given that the natural raw materials used for cement production are being depleted, the recycling of MSWI bottom ash for the application as building materials is meaningful and promising. The feasibility of using MSWI bottom ash as mineral additives in concrete has been demonstrated in the literature. In this research, as-received MSWI bottom ash has high mineral content and shows stable leaching behaviour. But, when used as cement substitute, the residual metallic Al in bottom ash always causes matrix swelling and strength loss by reacting with Ca(OH)2 and releasing H2 gas. In this research, dry and wet pretreatment methods were performed to remove the metallic Al in as-received bottom ash (0- 2mm). The results show that both of these two methods are effective. When comparing these two methods, wet method is time-consuming but can remove the metallic Al completely; dry method is fast but always has limitation that it can only reduce the metallic Al content by 80%. Regarding compressive strength, the decrease introduced by 10% dry-treated bottom replacement in cement paste is less than that of wet-treated bottom ash. The lower strength development observed in wet-treated bottom ash blended cement may be due to the removal of soluble reactive phases during the treatment. @en

This study investigates the effectiveness of metakaolin (MK)in mitigating the autogenous shrinkage of alkali-activated slag (AAS). It is found that the autogenous shrinkage of AAS paste can be reduced by 40% and 50% when replacing 10% and 20% slag with MK, respectively. By providing additional Si and Al, and decreasing the pH of the pore solution, the incorporation of MK retards the formation of aluminium-modified calcium silicate hydrate (CASH)gels, the main reaction products in the studied pastes. The chemical shrinkage and pore refinement are consequently mitigated, resulting in a substantial reduction in the pore pressure. Meanwhile, the elastic modulus of AAS paste is only slightly influenced after MK addition. As a result, the autogenous shrinkage of AAS is significantly mitigated by incorporating MK. In addition, the introduction of MK would extend the setting time, slightly decrease the compressive strength, but greatly increase the flexural strength of AAS.

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